$1,000 x 5% x 3 years
- Ending balance
- $1,150.00
- Principal
- $1,000.00
- Time
- 3 years
This is simple principal x rate x time math. It is not APR, APY, compound interest, daily balance billing, amortization, a bank disclosure, or a lender payoff quote.
Interest Calculator
Compare simple interest and compound interest from principal, annual interest rate, time in years, compounding frequency, and monthly deposits.
Estimate, not advice Payment or total shown Example inputs Tab-only history
Formula steps
- Convert 5% to decimal rate 0.05.
- Multiply principal by annual interest rate and time in years.
- Add interest to principal for the ending balance.
How to use the Interest Calculator
- Choose Simple when the question is principal x annual interest rate x time.
- Choose Compound when interest gets added back to the balance and can earn more interest later.
- Enter principal, annual interest rate, time in years, and only the compounding or monthly deposit fields your selected mode asks for.
- Calculate, then compare interest, ending balance, total contributions, and effective annual rate before trusting the estimate as a real loan, bank, or investment number.
What people use it for
Compare simple interest with compound interest.
Estimate interest earned on savings or interest charged on a balance.
Test how contribution size and time change compound growth.
Check whether a question belongs in the simple mode, compound mode, investment calculator, or loan calculator.
Quick examples
Simple interest
$1,000 at 5% for 3 years$150 interest and $1,150 ending balance
Compound growth
$2,500 at 5% for 8 years, compounded quarterlyAbout $3,720.33 ending balance
Monthly deposits
$1,000 plus $100/month at 6% for 10 yearsAbout $18,207.33 ending balance
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Interest Calculator See slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- Finance Browse related calculators and utilities in the same category.
- Calculator and utility guides Find more guides that use real tool inputs and example numbers.
- All free tools Search every live tool, converter, calculator, AI helper, and browser utility.
Frequently asked questions
Plain-language answers about when to use the estimate, what your numbers mean, what is left out, and how privacy works.
When should I use the Interest Calculator?
Use it when you want to test the exact inputs on this page: Compare simple interest with compound interest. Estimate interest earned on savings or interest charged on a balance. The result is a check against your assumptions, not proof that a lender, tax app, broker, platform, or provider will use the same number.
What do the main Interest Calculator inputs mean?
Principal means the starting amount before new interest or deposits are added. Annual interest rate means the yearly rate entered as a normal percent, such as 5 for 5%. Time in years means how long the estimate runs. Use 1.5 for 18 months or 0.25 for 3 months. Compounding frequency means how often interest is added back to the balance in compound mode. Monthly deposits means extra money added each month in compound mode.
Should I choose simple or compound interest?
Choose simple interest when interest is based only on the original principal. Choose compound interest when interest gets added back to the balance and can earn more interest later.
Why does the compound result grow faster?
Compound interest starts each new period from a bigger balance. For example, $2,500 at 5% for 8 years with quarterly compounding grows to about $3,720.33 before taxes, fees, or withdrawals.
Is annual interest rate the same as APR or APY?
No. The annual interest rate is the rate used by this calculator. APR can include certain loan fees, and APY reflects compounding on deposit accounts. Check the real disclosure when the exact legal or bank number matters.
What is the Interest Calculator doing with my numbers?
In plain language: Simple interest multiplies principal by annual interest rate and time. Compound interest grows the balance by the selected compounding frequency, then adds monthly deposits in the estimate. If the answer looks strange, check that the rate is annual, the time is in years, and the compound mode uses the compounding frequency you meant.
How should I read the Interest Calculator answer?
In simple mode, read interest and ending balance separately. In compound mode, compare ending balance, total contributions, estimated interest, and effective annual rate so deposits are not confused with growth.
What does this estimate leave out?
This is interest math only. It does not include APR fees, taxes, penalties, minimum balances, bank APY rules, investment risk, loan payment schedules, daily balance billing, promotional rates, or lender disclosures. For loans, compare the lender APR and payment schedule. For bank accounts, compare the stated APY and account rules. For investing, remember the return is not guaranteed.
What should I double-check before copying the result?
Double-check annual rate, time in years, compounding frequency, and whether you are trying to estimate savings growth, loan interest, APR, APY, or investment return.
Does the site save my finance inputs?
No. The calculator runs in your browser tab. Recent answers stay only on the page while you use it, and they are not sent to a server.
Related tools
Compound Interest Calculator Estimate compound growth with deposits, rate, time, and compounding frequency. Open Investment Calculator Project investment growth from starting money, monthly deposits, return, and time. Open Interest Rate Calculator Find the rate hidden inside a fixed loan payment quote. Open